One proposed structure of an internal combustion engine system varies the open-close timing of an intake valve to freely change a relative phase difference between the open-close timing of an exhaust valve and the open-close timing of the intake vale within a predetermined angle range. A phase angle having a least overlap between the open timing of the exhaust valve and the close timing of the intake valve is learnt as a most delayed phase angle.
Patent Document 1: Japanese Patent Laid-Open No. 2003-120374